Conventional automotive alternators include: a rotor that has: a pair of cores; a rotating shaft that is inserted into and fixed to a central portion of the cores; and excitation current supply slip rings that are fitted onto and fixed to the rotating shaft; a stator that is disposed on an outer circumference of the rotor; and a bracket that is disposed so as to surround the rotor and the stator, the rotor is rotatably supported in the bracket by means of bearings, cooling fans are mounted to two end surfaces of the rotor, a plurality of air intake apertures are disposed on an end portion of the bracket, a plurality of air discharge apertures are disposed on an outer circumferential portion of the bracket, and are configured such that internal portions of the alternator are ventilated and cooled by the cooling fans by rotation of the rotor (see Patent Literature 1, for example).
In these conventional automotive alternator cooling fans, loud noise that has frequencies that are integral multiples of the rotational frequency that arises due to fan blade end surfaces chopping the air has been reduced by mounting ring-shaped fan guides to the fan blade end surfaces on opposite sides from mounting sides (“tip sides”). Fan blade area has also been expanded by extending leading edge positions of the fan blades on the fan mounting side (“hub side”) closer to the rotating shaft, and reducing fan height gradually toward the rotating shaft, to increase the fan airflow rate and improve cooling performance. In addition, fan noise has been reduced without reducing the flow rate by giving the trailing edge positions of the fan blades an inclined shape on an air discharge side without changing the trailing edge positions of the fan blades on an opposite side from the mounting side.